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Thursday, July 10, 2008

Driving Less

The signs that Americans are driving less are everywhere. From headlines such as, "Gas Prices Spur Drivers to Cut Use to Five-Year Low", to increasing ridership on mass-transit systems and TV news segments on the growing numbers of folks bicycling to work, we see $4 gasoline doing what $3 fuel didn't: deliver a meaningful conservation response. But before we pat ourselves on the back for the DOE report that gasoline demand has fallen by 3% compared to last year, we should review a somewhat longer stretch of our recent history of fuel consumption and vehicle miles traveled. It suggests that the current decline, abetted by a weak economy, barely scratches the surface of our per-capita fuel consumption increase since 1995.

Conventional wisdom blames the SUV fad for most of the increase in US oil consumption in the last decade or so. But while rising sales of large SUVs in that period certainly helped to stall the positive trend of passenger car fuel economy, the bigger culprit has been the heretofore steady growth in vehicle miles traveled (VMT.) Between 1995 and 2005 this statistic grew by 23%, slightly more than the 21% increase in gasoline and diesel fuel consumption, and ahead of the 19% expansion of our car and light truck fleet. By comparison, during this period the US population grew by about 13%. In other words, Americans have been driving more cars, and on average driving them farther each year, than in 1995, accounting for more of the accompanying increase in fuel consumption than SUVs. This year's 2% decline in VMT compared to last year's record figure only erases part of the roughly 10% per capita growth of average annual miles driven since 1995. If we unraveled the rest of that growth, we could reduce US gasoline consumption by another 8% without any contribution from the higher fuel economy of the new cars consumers are now choosing. That equates to more than twice as much oil as our use of ethanol will save this year.

I don't pretend that conservation on that scale would be easy or costless. Some portion of the increase in VMT is structural, in the form of workers traveling longer distances from communities beyond the traditional suburbs. Much of the rest is associated with some sort of economic activity, including delivering goods and taking children to daycare or activities. The main advantage of this kind of conservation is that, at least in principle, it can occur much more rapidly than the efficiency gains from the gradual turnover of the vehicle fleet to smaller cars and a larger number of hybrids and alternative fuel vehicles.

It remains to be seen whether the fuel savings we are now observing will persist and expand, level out, or rebound. The first appearances of $2 gasoline in 2004 and $3 gasoline in 2005 delivered milder shocks to a healthier economy, slowing the growth of gasoline demand but not reversing it in the way that sustained $4 fuel has. That result could be put to the test, if oil prices continue to slide from their $145 high last week, or once the economy finally starts to improve. In the meantime, the scope for further behavior-based conservation remains significant.